The term "Financial Times 100" refers to the Financial Times Stock Exchange 100 Index, universally known as the FTSE 100. Often colloquially called the "Footsie," it is the most recognized benchmark for the performance of the United Kingdom’s equity market. Launched on January 3, 1984, it serves as a barometer not only for the health of large-cap UK-listed companies but also as a significant indicator of global economic trends, given the multinational nature of its constituents.

Defining the FTSE 100 and Its Origins

The FTSE 100 is a share index of the 100 largest companies by market capitalization listed on the London Stock Exchange (LSE). The name originated from a joint venture between the Financial Times (FT) and the London Stock Exchange (SE), hence the acronym "FTSE." While it is owned and maintained today by FTSE Russell, a subsidiary of the London Stock Exchange Group, the historical connection to the Financial Times remains embedded in its name.

At its inception in early 1984, the index was given a base value of 1,000 points. Since then, it has evolved into a multi-trillion-pound ecosystem. As of mid-2025, the total market capitalization of the index exceeds £2.1 trillion. It is important to distinguish the FTSE 100 from other indices in the series, such as the FTSE 250 (which tracks the next 250 largest companies) and the FTSE All-Share (a comprehensive index representing roughly 98% of the UK's market value).

The Internal Mechanics of Market Capitalisation Weighting

The FTSE 100 operates on a market-capitalization-weighted basis. This means that larger companies have a disproportionately greater impact on the index's movement than smaller ones. For example, a 1% price fluctuation in a giant like Shell or AstraZeneca will move the entire index significantly more than the same percentage change in a smaller constituent near the bottom of the list.

The Index Calculation Formula

The calculation of the index value is continuous during trading hours (8:00 AM to 4:30 PM London time). The basic formula involves summing the market values of all 100 companies and dividing that total by a specific "index divisor."

The market value for each company is calculated by multiplying its current share price by the number of shares in issue that are available for public trading—this is known as the "free-float" adjustment. The free-float factor ensures that shares held by governments or founding families, which are not readily tradable, do not artificially inflate a company's influence on the index.

The Role of the Index Divisor

The divisor is a crucial mathematical tool used to maintain the continuity of the index. Without it, events like new share issuances, company mergers, or the replacement of a constituent would cause the index level to jump or drop regardless of actual market sentiment. The divisor is adjusted during these corporate actions to ensure that the index value reflects only the changes in market prices.

Sector Diversification and Key Constituents in 2025

The FTSE 100 is often characterized by its heavy concentration in "old economy" sectors, such as banking, energy, and mining. However, as of 2025, the index shows a more nuanced distribution across 18 Industry Classification Benchmark (ICB) supersectors.

Dominant Industry Sectors

In our observation of the 2025 market landscape, four key sectors account for approximately 50% of the index's total capitalisation:

  1. Banks: Led by giants like HSBC Holdings, the banking sector remains a cornerstone of the index. In 2025, HSBC alone represents nearly 8% of the total index weight, reflecting its role as a global financial powerhouse.
  2. Healthcare: AstraZeneca and GSK are the primary drivers here. AstraZeneca, in particular, has maintained its status as one of the most valuable companies on the LSE, often vying for the top spot.
  3. Energy: This sector is dominated by Shell and BP. Their performance is closely tied to global oil and gas prices, making the FTSE 100 sensitive to geopolitical shifts in energy markets.
  4. Industrial Goods and Services: This broad category includes aerospace leaders like Rolls-Royce Holdings, which saw a significant resurgence in valuation throughout 2024 and 2025 due to increased demand in the civil aviation and defense sectors.

Top Constituents as of Late 2025

As of September 2025, the "Big Five" companies—HSBC, AstraZeneca, Shell, Unilever, and Rolls-Royce—collectively represent over 31% of the index weight. This concentration highlights why professional analysts focus so heavily on these specific entities when predicting index movements. Unilever, for instance, provides a stable consumer-staple anchor, while the volatility of Shell provides the index's growth (or contraction) "engine" during energy cycles.

The Quarterly Review and the 90/110 Rule

The makeup of the FTSE 100 is not static. Every three months (March, June, September, and December), the FTSE Russell committee conducts a review to ensure the index accurately represents the 100 largest qualifying companies. This process is governed by specific rules to prevent frequent "churn" or excessive volatility in the index's composition.

Promotion and Relegation Criteria

A company is not automatically removed the moment it drops to the 101st largest. Instead, the "90/110 Rule" is applied:

  • Promotion: A company in the FTSE 250 will be promoted to the FTSE 100 if its market capitalization rises to the 90th position or higher among all eligible companies.
  • Relegation: A current FTSE 100 constituent will be demoted to the FTSE 250 if its market capitalization falls to the 111th position or lower.

This buffer zone prevents companies near the boundary from constantly switching between indices due to minor daily price fluctuations. When a company is promoted or demoted, institutional investors who track the index (index funds) must rebalance their portfolios, which often leads to high trading volumes for the affected stocks on the day the changes take effect.

Historical Milestones and Market Volatility

Reviewing the history of the FTSE 100 reveals its resilience and its sensitivity to global crises.

The Early Years and Black Monday

Launched in 1984, the index quickly faced its first major test during the "Black Monday" crash of October 1987. In just two days, the index plummeted over 21%. Despite this, the privatization era of the 1980s—which saw state-owned enterprises like British Telecom and British Gas join the market—fueled long-term growth.

The Dot-com Bubble and the 1999 Peak

The index reached a significant milestone on December 30, 1999, closing at 6,930.2. At the time, this was a record high driven by the irrational exuberance of the technology, media, and telecommunications (TMT) boom. When the bubble burst, it took years for the index to recover those levels.

The 2024-2025 Structural Shift

A notable trend observed in 2024 was the delisting of several major companies from the LSE in favor of the New York Stock Exchange (NYSE). Companies like CRH and Flutter Entertainment moved their primary listings, citing higher valuations and deeper pools of capital in the United States. This "brain drain" led to concerns about the long-term competitiveness of the London market. However, in 2025, the index rebounded with a year-to-date total return of approximately 17.7% by September, suggesting that the remaining constituents—particularly in financials and aerospace—remained robust.

Is the FTSE 100 a Mirror of the UK Economy?

A common misconception is that the FTSE 100 is a direct reflection of the UK’s domestic economic health. In reality, it is more of a global index that happens to be listed in London.

The Global Revenue Stream

Research indicates that roughly 70% to 80% of the revenues generated by FTSE 100 companies come from outside the United Kingdom. Companies like Shell, Rio Tinto, and HSBC operate in dozens of countries. Therefore, the index is often more influenced by the strength of the US Dollar, Chinese industrial demand, or global interest rates than by UK GDP growth or domestic consumer spending.

Currency Sensitivity

Because many of its constituents earn in Dollars or Euros but report their financials in Sterling, the FTSE 100 often exhibits an inverse relationship with the British Pound (GBP). When the Pound weakens, the value of overseas earnings increases when converted back to Sterling, often pushing the index higher. Conversely, a strong Pound can act as a headwind for the index's performance. For a more accurate gauge of the domestic UK economy, analysts typically look at the FTSE 250, which contains companies with a much higher percentage of UK-based revenue.

Strategies for Investing in the FTSE 100

Since the FTSE 100 is an index, it is a mathematical construct and cannot be bought directly. Instead, investors use derivative products or tracking funds.

Exchange-Traded Funds (ETFs)

ETFs are the most popular vehicle for retail and institutional investors alike. These funds hold shares in all 100 companies in the same proportion as the index. Based on our analysis of the current market, some of the most liquid options in 2025 include:

  • iShares Core FTSE 100 UCITS ETF: Known for its low expense ratio and high liquidity.
  • Vanguard FTSE 100 UCITS ETF: A staple for long-term "buy and hold" investors.

Index Funds and Derivatives

For those who do not require the real-time trading capabilities of an ETF, traditional index mutual funds offer a way to gain exposure at a low cost. Additionally, the London International Financial Futures and Options Exchange (LIFFE) provides futures and options contracts based on the FTSE 100, which are used by professional traders to hedge against market downturns or speculate on short-term movements.

Performance Analysis: 2025 Context

In the current fiscal year of 2025, the FTSE 100 has demonstrated surprising strength despite high global interest rates. The dividend yield remains a significant attraction for income-seeking investors. As of late 2025, the average dividend yield for the index sits at approximately 3.27%, which is considerably higher than many of its international counterparts like the S&P 500.

While the S&P 500 is often driven by high-growth technology stocks (the "Magnificent Seven"), the FTSE 100 offers a "value" proposition. It trades at a lower price-to-earnings (P/E) ratio, making it attractive to investors who are wary of tech valuations and prefer the stability of cash-generative businesses in healthcare and banking.

Summary of the FTSE 100 Ecosystem

The FTSE 100 is a complex, evolving entity that represents the pinnacle of corporate achievement on the London Stock Exchange. From its origins as a joint venture in 1984 to its current status as a global investment titan, it remains the primary reference point for UK equity performance. Its heavy weighting in multinational "blue-chip" companies provides a unique blend of global exposure and dividend income, even if it does not always move in lockstep with the domestic UK economy.

Key Takeaways

  • Identity: "Financial Times 100" is the FTSE 100, managed by FTSE Russell.
  • Weighting: It uses a free-float market-cap weighting system.
  • Composition: 100 largest LSE-listed companies; reviewed quarterly.
  • Global Nature: Approximately 75% of revenue is earned outside the UK.
  • Top Sectors: Financials, Energy, Healthcare, and Industrial Goods.
  • Investment: Most easily accessed via UCITS ETFs.

Frequently Asked Questions

What is the difference between the FTSE 100 and the Dow Jones?

While both are flagship indices, the Dow Jones Industrial Average (DJIA) consists of only 30 US companies and is price-weighted. The FTSE 100 consists of 100 companies and is market-cap-weighted, making it more similar in structure to the S&P 500.

Why is it called the "Footsie"?

"Footsie" is a phonetic play on the acronym FTSE (F-T-S-E). It has become the standard informal name used by traders, financial journalists, and the public.

What happens if a company in the FTSE 100 goes bankrupt?

If a constituent company fails or is delisted, it is removed from the index immediately. The FTSE Russell committee will then select the largest company from the "reserve list" (usually the highest-ranking company in the FTSE 250) to take its place, and the index divisor is adjusted to maintain continuity.

Does the FTSE 100 include companies like Apple or Amazon?

No. While Apple and Amazon are among the largest companies globally, they are primarily listed on the NASDAQ in the United States. To be in the FTSE 100, a company must have a full listing on the London Stock Exchange.

How often does the FTSE 100 change its constituents?

The index undergoes a formal review four times a year. While the core "Big Five" rarely change, companies at the bottom of the rankings are frequently promoted or demoted based on their market performance over the preceding quarter.